1. Field of the Invention
The present invention relates to a magnetic head for reproducing magnetically recorded information, and a magnetic recording system equipped with the magnetic head. Specifically, the present invention relates to a magnetic reproduction head with especially high output reproduction, and a magnetic recording system equipped with the magnetic reproduction head.
2. Description of the Related Art
In the magnetic disk device field, the magnetoresistive sensor using the magnetoresistive effect with variable electric resistance in accordance with the change in the external magnetic field has been well known as the high-performance magnetic field sensor. The aforementioned magnetoresistive sensor has been put into practical use as a reproduction element for detecting the signal magnetic field from the magnetic recording medium in the magnetic head as the main component of the magnetic recording/reproduction system.
The recording density of the magnetic recording/reproduction system has been improved at a high pace, requiring the magnetic head to have the minimized track width T while establishing the high performance with respect to such properties as recording and reproducing. The reproducing performance has been improved to have higher sensitivity by developing the MR head using the magnetoresistive effect. In the case of the low recording density of several Gb/in2, the magnetic signal on the recording medium is converted into the electric signal using the anisotropic magnetoresistive effect (AMR). When the recording density is increased to exceed the aforementioned level, Giant Magnetoresistive effect (GMR) with higher sensitivity is employed.
The process for applying the detection current in the direction substantially perpendicular to the film surface, that is, Current-Perpendicular-to-Plane (CPP) process as the advantageous way to achieve the high sensitivity has been developed accompanied with the reduction in the distance (reproducing gap length) between the upper magnetic shield layer and the lower magnetic shield layer so as to meet the needs of further higher recording density. The magnetic reproduction head using CPP-GMR and Tunneling Magnetoresistive effect (TMR) has been introduced.
Referring to FIGS. 1 and 2, the basic structure of the CPP type magnetic reproduction head will be described. FIG. 1 shows a cross section (cross section perpendicular to the direction of the element height) in parallel with the plane opposite the medium of the CPP type magnetic reproduction head. X-axis, Y-axis, and Z-axis shown in FIG. 1 correspond to directions of the track width, element height, and thickness of the magnetoresistive film, respectively. The X-axis, Y-axis, and Z-axis shown in subsequent drawings have the same axes as those shown in FIG. 1. A refill film 1 in the track width is formed in contact with a wall surface of a magnetoresistive film 3 in the track width direction. A longitudinal bias application layer or a side shield layer 5 is formed on the refill film 1. FIG. 1 shows an upper magnetic shield layer 2 and a lower magnetic shield layer 4. FIG. 2 is a sectional view of the CPP type magnetic reproduction head in the element height direction taken along line a-a′ of FIG. 1. A medium opposing surface 112 of the magnetic reproduction head is shown at the right side of FIG. 2. Similarly to the track width direction, a refill film 6 in the element height direction is formed in contact with the wall surface of the magnetoresistive element 3. Both the refill film 1 in the track width direction and the refill film 6 in the element height direction are formed mainly of the alumina as the insulating film.
Normally the CPP type magnetic reproduction head is produced such that the upper and the lower magnetic shield layers 2 and 4 are electrically in contact with the magnetoresistive film 3 for reducing the reproducing gap length as small as possible. Each of the upper and the lower magnetic shield layers 2 and 4 serves as an electrode for applying the electric current to the magnetoresistive film 3. The circuit which short-circuits between the upper and the lower magnetic shield layers 2 and 4 besides the magnetoresistive film 3 may form a leak passage of the detection current, thus causing drop in the output.
The side wall surface of the magnetoresistive film 3 is considered as the location on which the short circuit is formed, which may be relevant to the process for producing the magnetic reproduction head. FIG. 3 shows two flowcharts showing steps of forming the CPP type magnetic reproduction head. The process for producing the magnetic reproduction head includes steps of forming the lower magnetic shield layer, forming the magnetoresistive film, patterning the magnetoresistive film, and forming the upper magnetic shield layer. The two processes shown in FIGS. 3A and 3B are different in the order of the steps for forming the element height of the magnetoresistive film, and forming the track width of the film. Those steps may be performed in an arbitrary order depending on the situation.
In the steps of forming the element height and the track width by patterning the magnetoresistive film, the magnetoresistive film 3 is formed on the lower magnetic shield layer 4 as shown in FIG. 4A, and then the magnetoresistive film 3 is protected with a resist mask 101 for forming the track width with a predetermined size, or a resist mask 111 for forming the element height as shown in FIG. 4B. Then the magnetoresistive film 3 has the unnecessary region etched away as shown in FIG. 4C. In the etching step, the etching is normally performed through the ion beam etching process using Ar ion, and through the RIE process using chlorine gas or CO gas. Subsequent to the etching step, the refill film 6 in the element height direction or the refill film 1 in the track width direction is formed as shown in FIG. 4D. Then the resist mask 101 or 111, and the unnecessary refill film are removed through the lift-off process as shown in FIG. 4E to form the element height or the track width of the magnetoresistive film 3. Although not shown in FIG. 4D, a side shield film or a longitudinal bias application layer is further formed on the refill film 1 in the track width direction in the step of forming the track width.
During the etching step shown in FIG. 4C, the subject to be etched is adhered to the wall surface of the magnetoresistive film 3 again, that is, so called reattachment occurs. The reattachment is a stack film formed of the metal for forming the magnetoresistive film 3 or the lower magnetic shield layer 4. The reattachment as the conductive material may form the leak passage of the detection current as described above.
Japanese Published Unexamined Patent Application No. 2003-86861 discloses the method for preventing the leakage of the detection current owing to the reattachment on the wall surface of the magnetoresistive film 3 in the track width direction by oxidizing the reattachment after etching when performing the step of forming the track width. The method allows the oxidized reattachment to be utilized as a portion of the refill film in the track width direction.
Japanese Published Unexamined Patent Application No. 2002-26423 discloses the method for removing the reattachment on the wall surface of the magnetoresistive film 3 by masking the magnetoresistive film 3 formed on the lower magnetic shield layer 4 into a predetermined shape with the resist mask 101 for forming the track width or the resist mask 111 for forming the element height to perform etching by projecting the ion beam at a first incident angle of θ1, and to further perform etching by projecting the ion beam at a second incident angle θ2 larger than the incident angle of θ1 (θ2>θ1) with respect to the magnetoresistive film 3. The incident angle herein denotes the angle defined by the normal of the substrate and the incident ion.
Japanese Published Unexamined Patent Application No. 2006-24294 discloses the advanced method for performing the two-stage etching process using two refill films having the hardness of the second refill film lower than that of the first refill film so as not to form the region resistant to the incident ion beam for removing the reattachment.
When the track width becomes 50 nanometers or less, the detection current still leaks even though the reattachment is oxidized after etching as disclosed in Japanese Published Unexamined Patent Application No. 2003-86861, or even though the advanced two-stage etching is performed as disclosed in Japanese Published Unexamined Patent Application No. 2006-24294.